In my opinion the latest version of this add-on works great in FF 51/Win10 configuration. You have to check "Remember me for 30 days" ticker AND add set FF to accept and keep cookies from https://evernote.com. Otherwise you will have to log in each time you start FF. With these options set, things works just fine. Clipping, saving PDFs, saving entire Gmail conversation - options I use the most. After successful clipping the note is immediately visible in the web interface and on my phone (after a sync). I give 4* because of the complications with staying logged in.